A biotoxin found in marine life off Southampton Town has prompted state officials to temporarily shut down harvesting of shellfish and meat-eating gastropods on 3,900 acres of water.

The temporary closure, effective Thursday, affects Shinnecock Bay west of the southbound lanes of the Ponquogue Bridge and east of the western side of the Post Lane Bridge in Quogue, said the state Department of Environmental Conservation.

The move comes after shellfish in Weesuck Creek in Southampton and Meetinghouse Creek in Riverhead tested positive for saxitoxin, a marine biotoxin that causes paralytic shellfish poisoning. Carnivorous gastropods, which includes whelks, conchs and moon snails, feed on shellfish and may build up biotoxins at levels that are dangerous to people who eat them.

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DEC officials said they will continue testing marine samples at 13 monitoring locations around the Island and reopen the waters when the toxin falls to safe levels.

A recorded message on which areas have been temporarily closed may be heard at 631-444-0480. Maps showing the off-limit areas can be seen at dec.ny.gov.